ABSTRACT Cachexia is a debilitating syndrome that results in severe, involuntary weight loss due to the depletion of skeletal muscle mass. This syndrome occurs in a majority of cancers and contributes to approximately a third of all cancer deaths. Currently, no effective therapy exists to combat this malignant disorder. For pancreatic cancer the potential benefit for effective cachexia therapies may be even greater than for other cachexia associated malignancies, since 90% of these patients lose on average 14% of their pre-illness weight, and cachexia dramatically limits their ability to tolerate surgery, chemo- or radiotherapy. New therapies will likely evolve from an enhanced understanding of the mechanisms leading to muscle wasting. Our recent efforts have focused on events that occur outside the myofiber in the muscle microenvironment. We showed that circulating tumor factors induce skeletal muscle damage leading to the activation of NF-kB in muscle progenitor cells that associated with an engaged regeneration program. However, regeneration is inhibited leading to muscle atrophy. We now find that NF-kB activation in muscle stem cells also promotes a local muscle inflammation, characterized by the production of cytokines and chemokines. These signals promote the recruitment of macrophages expressing M1 inflammatory and M2 anti-inflammatory makers. The goal of this application is to test the hypothesis that NF-kB in muscle progenitor cells regulates this local inflammatory environment that contributes to muscle atrophy. Towards this goal we seek to perform the following two specific aims: 1) Determine how NF-kB regulates local muscle inflammation in cancer cachexia; and 2) Elucidate the phenotype and relevance of macrophages in cancer-induced muscle wasting. Achieving this goal will not only provide insight into the mechanisms and therapeutic targets of muscle wasting in cancer, but will also broaden an area of cachexia research that is currently underexplored.